Control system



Dec. 3, 1935. RHEA r L 2,023,243

CONTROL SYSTEM Filed June 8, 1933 2 Sheets-Sheet 1 Figl.

- 3, 1935- T. R. RHEA ET AL CONTROL SYSTEM Filed June 8, 1933 2Sheets-Sheet 2 VARIABLE SPEED DEVICE Fig. 2.

i 5 e W 6 K r a n mfimww fim fiA A mmw AQI w Tm T Patented Dec. 3, 1935UNITED STATES PATENT OFFICE CONTROL SYSTEM Application June 8, 1933,Serial No. 674,894

12 Claims.

Our invention relates to control systems, more particularly to the speedcontrol of machines of the type arranged for operation on a length ofmaterial, and has for an object the provision of such a control systemwhich is reliable and eflicient in operation.

Although it obviously has other applications, our invention isparticularly useful in connection with flying shears of the type usedfor severing bars of metal. These bars of metal are generally driventhrough the flying shear after the rolling mill has reduced them topredetermined dimensions.

Heretofore, the first crop from each piece of stock or length of metalhas represented a loss because the length of the first crop has beenindeterminate; that is to say, the stock may enter the shear while its'knives are in some indeterminate angular position. Therefore the lengthof the first crop may vary from a few inches to the full length of thecut. By the law of averages it may be assumed therefore that the averagelength of the first crop may equal approximately one-half the length ofthe cut. The loss in tonnage represented in the course of the days runbecomes quite appreciable, and it is a further object of our inventionto eliminate this loss.

It has been proposed to control the length of the first crop by stoppingthe rotary shear with the blades occupying a definite angular positionafter the cutting of each bar has been completed. The next bar as itapproached the shear was arranged to control the energi'zation of theshear motor, so that the blades or knives of the shear occupied apredetermined position after the bar entered the shear. Much is yet tobe desired in this type of control, because driving motors of verysubstantial sizes are required in order to accelerate the rotatingportion of the shear to full speed in the time which-is available. Theproblem becomes increasingly more difilcult as the delivery speed of thestock is increased. The time for accelerating the motors is furtherdiminished if the finishing stand is located close to the shears.v

In carrying out our invention, in one form thereof, a flying shear isdriven continuously, and means are provided whereby the blades of theshear will occupy a definite angular position when the front end of abar reaches a definite position in its travel. More specifically, weprovide a position-determining device arranged to be accelerated from adefinite angular position whenever the leading end of a bar of metalarrives at a predetermined distance from the shear. This definiteangular position corresponds to the position that the blades shouldoccupy. A second position-determining device is driven in angularagreement with the blades 5 of the shear. By means of adifferential-positioning device the angular position of the blades iscompared with the position which the blades should occupy. Thediflferential-positioning device is arranged to accelerate or to retardtemporarily the shear driving motor so as to eliminate the angulardisplacement, or in other words to bring the blades into the positionwhich they should occupy. The differential-positioning device thereafterserves to maintain the speed of the shear so that the blades thereafterare maintained in the proper position to sever the bar intopredetermined lengths.

It will be understood that in accordance with our invention the forceinvolved to accelerate or go ity of the machines is obtained and theoperatg ing costs are correspondingly less.

' For a more complete understanding of our invention reference should behad to the drawings wherein we have shown diagrammatically in Fig. 1 ourinvention applied to the control of a flying shear while in Fig. 2 wehave shown a modified form of our invention.

Referring to the drawings, we have shown our invention in one form asapplied to a direct current motor l0 connected by the gearing ii to 5drive a flying shear l2. The shear l2 consists of two revolving drums l3and it, each of which carries, respectively, the blades l6 and I1.

Steel bars or other types of stock, for example the bar in, are arrangedto be driven from a rolling mill 22 to the rotary shear !2. The rollingmill 22 is driven by a motor 23. Inasmuch as the last operation in theproduction of steel bars of a given dimension is completed before thebar is cut into predetermined lengths, it will be understood that the,rolling mill 22 represents the last finishing stand. As long as the bar20 is in the rolls of the finishing stand 22, the speed of the bar isdetermined entirely by the speed at which the motor 23 drives the rolls.However, after the go tail end of the bar 20 leaves the finishing stand22 it is obvious that its speed no longer depends on the speed of themotor 23. Therefore, in order to maintain the accuracy of the cuts apair of pinch rolls 25 are provided adjacent the shear l2. The pinchrolls 25 are drlven by the motor I 0 the connection including a variablespeed drive 26 and the gears I l and 21. By shifting the belt 28 on thecone pulleys 29 and 38 of the variable speed drive the speed of thepinch rolls 25 may be adjusted to correspond to the proper deliveryspeed of the stock or bar 28. The length of each cut is determined bythe ratio of the speed of the mill and of the shear l2, and after thebar leaves the finishing stand by the ratio of the speed of the pinchrolls 25 and of the shear l2. Therefore,.a, movable pointer 32 connectedto the belt 28 is arranged to be movable over a calibrated scale 34,calibrated in terms of the length of out. It will be assumed that in theposition shown the length of out is 10 feet. The speed of the motor 23driving the rolls of the finishing stand 22 is now adjusted so that thedelivery speed of the bar 20 from the finishing stand will correspondwith the speed. at which the pinch rolls 25 will drive the bar throughthe shear. To assist in making this adjustment the speed indicator 40 isprovided with a coil 4| connected in circuit with a tachometer generator42. A second coil 44 on the indicator 40 is connected across thearmature of a second tachometer generator 45 driven by the motor 23. Thecoils 4| and 44 act differentially on the pointer 46 of the indicator.When the speed of the rolls of the finishing stand corresponds to thespeed of the pinch rolls 25, the pointer 46 occupies a. centralposition. As shown the speed of the motor 23 is adjusted by means of arheostat 49 connected in circuit with the separately excited fieldwinding 58 provided for the motor.

In accordance with the present invention the motor I0 is energized todrive the shear I2 continuously. Under these conditions in order topredetermine the length of the first crop made by the shear, it isnecessary to insure that the blades l6 and I1 occupy a definite angularposition (which angular position will insure a predetermined length ofthe first crop) as the leading end of the bar 20 arrives at the shear.It will further be understood that if the bar 28 is driven at apredeterminedspeed by the rolls of the finishing stand 22 and by thepinch rolls 25, the angular positions that the blades l6 and I! shouldoccupy as the leading end of the bar 20 leaves the finishing stand canreadily be determined. Therefore, the angular positions which the bladesl6 and I1 sham occupy are compared with the angular positions that theyactually occupy as the leading end of the bar leaves the finishing stand22 and the difference, or the angular displacement, is eliminated byretarding or accelerating the motor l0 until the blades l6 and Il occupythe predetermined angular positions. Iri'this manner the length of thefirst crop is determined. In Fig. 1 this is accomplished by providing aposition-determining device 55, the rotor of which is normallymaintained in a predetermined position by means ofa disk 56 providedwith magnetic inserts 51. The magnetic inserts are arranged to beattracted by the coils 58 so that the rotor of the position-determiningdevice 55 is always brought to a standstill in a predetermined position.This means for bringing the rotor of the position determining device toa standstill in a predetermined angular position forms no part of ourinvention, and it is described and claimed in a copending application ofStewart H. White, Serial No. 674,890, filed June 8, 1933, assigned tothe same assignee as this application.

The position-determining device itself is provided with a distributedthree-circuit rotor .winding (not shown) and with a distributedthreecircuit stator winding (not shown). Devices of this type aredescribed and claimed in U. S. Patent 1,612,11'7-Hewlett et al.December'28, 1926.

The rotor of the device 55 is arranged to be connected to the motor 23by means of a magnetic clutch 60 provided with an operating coil. 6|.Between the magnetic clutch and the motor 23 there is interposed avariable speed'mechanism 63 consisting of cone pulleys 64 and 65, a belt66 and a belt shifter 61. The variable speed mechanism 63 is driven fromthe motor 23 by means of the gears 68 The rotor circuit of the device 55is connected to the stator circuit of a second device 18. This devicehas a single circuit rotor winding (not shown), the terminals of whichare connected to a single phase source of supply represented by thereference numeral I2. This winding is mounted on a shaft 13 providedwith an operating handle 14 whereby the inductive relation of the rotorwinding with respect to the stator winding can be varied as may bedesired. This device is described and claimed in U. S. Patent 1,637,039to Hewlett et al. dated July 26, 1927. A position-sending device 16 isdriven by the shear driving motor 10 and is of a construction similar tothe device 18. Its single circuit rotor winding (not shown) is energizedby the single phase, alternating current source of supply 12,30 whileits three-circuit stator winding is connected to the three-circuit rotorwinding of a difierential receiving device 18. ,A three-circuit statorwinding (not shown) of the device 18 is connected to the stator windingof the device 55. The position that the blades of the shear shouldoccupy when the leading end of the bar 28 arrives at a predetermineddistance from the shear I2 is determined by the device 55. When the barreaches this predetermined point, the magnetic clutch 60 is energized torotate the position-determining device 55 at the same speed as that atwhich the shears should rotate. This speed relation is obtained by meansof the mechanism 63. In order to assist in fixing this speed adifferential receiving device 80 is provided and has its threecircuitstator winding connected to the stator winding of the position-sendingdevice 16, while its three-circuit rotor winding is connected to thethree-circuit stator winding (not shown) of a device 82 provided with asingle circuit rotor winding (not shown) arranged to be energized fromthe alternating current source of supply 12. The belt shifter 61 isoperated until a pointer 84 driven by the rotor of the device 80 remainsstationary. As long as there is a difference in speed between the rotorsof the devices 16 and 82 the pointer 84 will rotate. As soon as itremains stationary, however, an indication is had that the belt 66 hasbeen properly adjusted. so A flag switch 86 is arranged to be operatedto closed circuit position whenever the leading end of a bar, forexample the bar 28, strikes the operating member 81 of the switch. Aspring 88 normally biases the switch to the open circuit po- 65 sition.Assuming that the bar 20 has closed the switch 86, it will be observedthat an energizing circuit is completed for the operating coil 89 of arelay 90. The relay 9!] is thereupon free to open its normally closedcontacts 9| to interrupt a nor- 7 mally energized circuit including thecoils 58 and to close its contacts 92 and 93. Consequent to the closingof the contacts 92 an energizing circuit is completed for the operatingcoil 6| of the clutch 60. The clutch thereupon connects the rotor 7 ofthe position-determining device 55 to the variable speed mechanism. Therotor of the positiondetermining device 55 will be rotated at the samespeed as the rotor of the position-sending device I6. It will beremembered that the rotor of the position-determining device 55 was heldstationary at the angular position that the blades I6 and II shouldoccupy when the leading end of the bar 20 operated the fiag switch.Consequently, if the blades i6 and I! are not in this predeterminedangular position the rotor of the position-sending device 16 will be ina difierent position with respect to its stator winding than is therotor of the device 55. Under these conditions it will be understoodthat the respective voltages applied to the difierential receivingdevice I8 are displaced with respect to each other, thereby moving therotor of the device I8 an amount proportional to the angle ofdisplacement between the two devices 55 and IS. The speed of the motorI0 is then varied until this angular difierence disappears. When therotors of the devices 55 and I6 are in angular agreement with eachother, the blades I6 and I1 occupy the predetermined angular positionswhich will result in a predetermined crop of the bar 20 when it arrivesat the shear I2.

The energization of a separately excited field winding 98 provided onthe motor I0 is controlled by means of a rheostat 99 and a motorgenerator set I00. A motor MI is energized from a suitable source ofdirect current supply. A generator I02 is provided with a pair of fieldwindings I04 and I05. The field winding I04 is connected by theconductor I00 to one side of the secondary winding I08 of a transformerI09 provided with a primary winding H0. The other side of the fieldwinding I04 is connected to the anode III of an electric valve H2. Thefield winding I05 is connected by conductor II3 to the other side of thetransformer secondary winding I08. The other side of the field windingis connected to an anode III of an electric valve H8. The valves H2 andI I8 are preferably of the type having an inert gas, such as mercuryvapor, within their envelopes. It will be understood that when therespective grids I20 and I2I of the valves H2 and H8 are madesufficiently positive with respect to the anodes, the valves becomeconductive.

The grid circuits of the valves include a translormer I23, the primaryof which is energized from the single circuit winding (not shown) of thedevice I25, the stator winding (not shown) being connected to thecontacts 93 of the relay and to the single phase source of supply I2.The rotor of the device I25 is mechanically connected to the rotor ofthe differential positiondetermining device I8. It will also be observedthat the primary winding IIO of the transformer I09 is arranged to heenergized by means of the contact 93 from the single phase source ofsupply I2. The cathodes I21 and I28 with their respective valves H2 andI I8 are energized from a suitable source of supply and are connected bymeans of the conductor I30 to the mid-point of the transformer secondarywinding I08 and also by corductor i3I to the mid-point of the secondarywinding of the transformer 23. The rotor of the device I25 norgnallyoccupies a position with respect to its stator winding such that novoltage is applied to the primary winding of the transformer I23.However, if an angular disagreement is indicated by the differentialdevice I8 it -will, of course, be understood that the rotor of thedevice I25 is moved from this neutral position.

The consequent change in the relative positions of the stator and rotorwindings causes a resultant voltage to be produced on the primarywinding of the transformer I23. The polarity of this voltage isdetermined by the direction of rotation of the rotor winding. If, forexample, the differential device 18 rotates the rotor of the device I25in a clockwise direction, the voltage applied to the primary of thewinding of the transformer I23 may cause a voltage to be produced on thegrid I2I which will render the valve II8'conductive. The movement of therotor of the device I25 in the opposite direction will then cause avoltageto be applied to the grid I20 of the valve I I2 to render thisvalve conductive. Accordingly, the field winding I04 will be energizedin a direction to produce a. voltage of one polarity on the generatorI02 and the field winding I05 is arranged to produce an oppositepolarity on the generator. Assuming now that the rotor of the device I25has moved in a clockwise direction to cause the valve H8 to becomeconductive, it will be observed that the field winding I05 will beenergized. The generator I02 will thereupon produce a voltage in adirection to reduce the voltage which is normally applied to the fieldwinding 98 of the motor I0 by the direct current source of supply. Thiscauses the motor I0 to increase its speed. As soon as the angulardisagreement between the position which the blades of the shear occupyand the position which they should occupy is eliminated, thedifferential device I8 moves the rotor of the device I25 to its neutralposition, and the valve H8 again becomes non-conductive. The voltage ofthe generator I02 disappears and the shears again rotate at their normalspeed. Assuming now that the angular disagreement is in the oppositedirection so that the difierential device I8 operates the rotor of thedevice I25 in a counter-clockwise direction, it will be seen that thevalve I I2 is rendered conductive. The resultant energization of thefield winding I04 causes the generator I02 to produce a voltage whichadds to that of the direct current supply. The increase in theexcitation produced by the field winding 98 decreases the speed of themotor I0 until the angular disagreement has been wiped out.

In addition to temporarily varying the speed of the shear driving motorI0 the speed modifying means also serves to maintain a predeterminedrelation between the speed of the shear and the speed of the rolls ofthe rolling mill 22. For example, if the speed of either the sheardriving motor I 0 or-the mill driving motor 23 should change after thebar has operated the flag switch 86, the differential device I8 willimmediately indicate the change in the relative speeds. The electricvalve speed controlling means will immediately function to varytemporarily the speed of the shear driving motor I0 so that the blades I6 and H of the shears I2 always occupy their predetermined positions.

If the first crop taken by the shear happens to be too long or tooshort, the handle I4 of the device I0 is rotated an amount which isestimated' to insure the desired length of crop. The result of rotatingthe rotor of the device I0 with respect to its stator is to change theelectrical relationship between the device 55 and the device I8 bycausing an angular displacement of the voltage which is applied to therotor of the device 55. This serves as the electrical equivalent ofactually changing the angular position from which the rotor of theposition-determining device 55 is accelerated. If'the crop of the firstle gth of material is greater or less than that de red, it will beunderstood that the handle 14 is again rotated for an estimatedcorrection. In ordinary practice it requires but a' few adjustments ofthe device 10 to obtain the desired length of the first crop.

Assuming now that the tail end of the bar 20 is leaving the flag switchit will be observed that the spring 88 operates to open the contacts06a. The opening of these contacts deenergizes the operating winding 89of the relay 90,'which relay after a. predetermined time intervaloperates to open its'contacts 92 and 93 and to close its contacts 9|.The opening of the contacts 92 deenergizes the clutch 60 while theopening of the contacts 93 deenergizes the speed controlling means.

Consequent to the closing of the contacts SI of the relay 60, the magnetcoils 58 are energized,

which coils serve to stop the disk 56 with the magnetic memberpositioned between the coils. The apparatus is now in readiness for thenext bar and functions in the same manner as we have just explained assoon as its leading end operates the flag switch 81.

The time delay openingof the relay 90 is accompiished by means of ashort circuited coil I35. By delaying the opening of the contacts 92 and93 of this relay more time is obtained for correcting the position ofthe shears. This additional time might be necessary in case it is founddesirable 'to locate the flag switch 81 not behind the finishing stand22, as shown, but ahead of it.

It will be remembered that the pinch rolls were provided to maintain thespeed of the bar 20 at proper value because the shears I2 were located asubstantial distance from the finishing stand 22. If the pinch rolls 25had not been provided the speed of the bar 20 would not have been fixedduring its whole travel from the finishing stand 22 to the shears I2. I

In Fig. 2 we have shown our invention in one form as applied to arolling mill wherein the shears I2 and the finishing stand 22 are spacedapart a short distance. Accordingly, the pinch rolls 25 have beenomitted and the motor I0 used to drive the rolls of the finishing stand22, is also used to drive the shear. As shown, the preceding stand I52is located a substantial distance from the last finishing stand 22 sothat suflicient time will elapse during the travel of the bar from onestand to the other to permit the adjustment of the shear blades.Assuming that the speed of the motor 23 driving the stand I52 is set ata predetermined speed with reference to rolls 22 and therefore to theshears I2, it will be observed that as, the leading end of the bar 20enters the stand I52 a relay I54, responsive to the current of the motor23, is operated to interrupt by means of its normally closed contactsI55 an energizing circuit for a coil I56 provided on a timing relay I51and to complete a circuit through its contacts I58 and through contactsI59 of the timing relay a circuit for the operating coil of the relay90. The timing relay I51 is provided with a short ciroulted coil I60which serves to maintain the timing relay closed for a time whichapproximates the time required for the bar 20 to travel from the standI52 to the-stand 22.

The position-determining device 55 is arranged to be operated from apredetermined position as in the case of Fig 2. In this form of ourinvention, however, a direct current generator I62 provided with aseparately excited field winding I63 adjusted by means of its fieldrheostat I66. In I i this manner the speed at which theposition-determining device 55 rotates can be adjusted so as tocorrespond to the speed of the shears I2.

The speed control means includes an electric valve I10 having its outputcircuit connected 10 through a variable resistance I1I, contacts 63 ofthe relay 90, field winding I12 of the generator I02, secondary windingI13 of transformer I14 and to the cathode I15 of the valve I10.Preferably the field winding I12 is connected so that iii the generatorI02 serves to increase the field excitation of the motor I0. The directcurrent output of the valve I10 is controlled by means of the device I25provided with a single circuit rotor winding and a three circuit statorwinding. By 2 means of a phase converting apparatus, shown ascapacitorI00 and reactor I82, the three circuit winding is directly connected tothe single phase source of supply 12.

This manner of controlling the electric valve 25 is fully described inU. S. Patent 1,655,036 to Alexanderson et al., January 3, 1928 and inthis specification will be briefly described by saying that the time ofstarting of current in electric valve I10 may be controlled for eachhalf cycle. Therefore; the average flow of current which may flowthrough the field winding I 12 is directly proportional to thediflerence in the angular positions of the rotors of the devices 55 and16. It follows that the change in speed of the driving motor I0 causedby the voltage generated by the booster generator I02 also varies inproportion to the angular disagreement between themtors of the devices55 and 16.- For example, if there is a substantial disagreement betweenthe 4 device 55 and the device 16 after the clutch 60 has operated toaccelerate the device 55 from the predetermined position, it will beunderstood that the voltages applied to the differential receivingdevice 10 are displaced a corresponding amount. Consequently, thedifferential device 18 rotates the rotor winding of the device I'25 anamount proportional to the displaced voltages. The result is a shift ofthe phase of thegrid voltage of the valve I10 with respect to its anodevoltage so that the valve I10 becomes conductive over a substantial partof each half cycle. The booster generator I02 thereupon increases theexcitation of the field winding 98 of the motor I0,

thereby decreasing its speed a substantial amount. As the blades I6 andI1 of the shears I 2 are operated into angular position the increasedexcitation produced by the generator I02 diminishes. When the bladesreach the positions which they should occupy as determined by the device55 and the setting of the device 10, the motor I0 is again rotating atits former speed but the shear blades I6 and I1 are now in theircorrected positions.

While we have shown a particular embodi- 65 ment of our invention, itwill be understood, of course, that we do not wish to be limited theretosince many modifications may be made, and we, therefore, contemplate bythe appended claims to cover any such modifications as fall within thetrue spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of theUnited States, is:

1. Means for controlling a machine arranged to perform operations on amoving strip of material i ment between the shear and said device fortemso that its operations occur at predetermined points on said strip,comprising driving means for said machine, driving means for said strip,means responsive to the position of said strip for indicating thedesired angular position of said ma chine when said strip is apredetermined distance from said machine, and means controlled by saidlast mentioned means for temporarily varying the speed of said machinewith respect to said strip so as to establish said desired angularposition of said machine.

2. The combination with a'rotary shear arranged to sever strips ofmaterial into predetermined lengths, of means for continuously drivingsaid shear, material driving means located a predetermined distance fromsaid shear for driving said material to said shear, means for indicatinga desired angular position of said shear when the leading end of saidmaterial is a predetermined distance'from said shear, and meanscontrolled by said last mentioned means for varying the angular positionof. said shear with respect to the leading end of said material untilsaid desired angular relation is obtained.

3. The combination with a rotary shear arranged to sever strips ofmaterial into predetermined lengths, of means for continuously drivingsaid shear, means located a predetermined distance from said shear fordriving said strip of 7 material to said shear, a position-determiningdevice normally at rest in a definite angular position, means responsiveto the travel of said strip for accelerating said device to the speed ofsaid shear, means responsive to the angular. disagreeporarily modifyingthe speed of said shear until said device and said shear are broughtinto angular' agreement and for maintaining said angular agreement.

4. Means for predetermining the length of the first cut of a strip ofmaterial arranged to be driven through a pair of rotary shearscomprising a motor for driving said shears continuously, aposition-determining device, a pilot motor arranged to accelerate saiddevice from a predetermined angular position to the speed of'saidshears, and means responsive to the angular difference between saiddevice and said shears for controlling the speed of said shears so as tobring said device and said shears into angular agree,- ment.

5. Means for controlling a machine arranged to perform operations on astrip of material so that its first operation occurs at a predeterminedpoint on said material comprising motor driving means for said machine,material driving means for said strip, a position-determining device,means for producing an electromotive force upon positional disagreementof said machine and said device corresponding in value and direction tothe amount and direction of. said positional disagreement, and a pair ofelectric valves responsive to said electromotive force for controllingsaid motor driving means so as to bring said machine into positionalagreement with said position-determining device.

6. Means for predetennining the length of the first crop of a strip ofmaterial arranged to be driven through a rotaryshear provided with apair of cutting blades, comprising a motor for driving said shear, speedcontrol means for said motor, a pair of driving rolls arranged apredetermined distance from said shear to drive said strip to saidshear, means for driving said rolls, a position-determining devicenormally at rest in an angular position corresponding to the angularposition which the blades of said shear should occupy when said stripenters said rolls, a pilot motor arranged to accelerate saidposition-determining device to a speed corresponding to the speed ofsaid shear, means responsive to the arrival of said strip between saiddriving rolls for connecting said pilot motor and saidpositiondetermining device, a position sending device driven by saidshear, a differential position-receiving device responsive to saidposition-determining device and to said position setting device foroperating said speed control means so as to bring said shears intopositional agreement with said position-determining device.

7. Means for controlling a machine arranged to perform operations on astrip of material so that its operation occurs at a predetermined pointon said material comprising motor driving means for said machine,driving means located a predetermined distance from said machine forsaid strip, a position-determining device, means for accelerating saidposition-determining device from a predetermined angular position to thespeed of said machine-whenever said strip of material enters saiddriving means, timing means therefor arranged to decelerate saidpositiondetermining device after a predetermined interval of time, andmeans for stopping said positiondetermining device in a predeterminedangular position.

8. In a system for maintaining a predetermined relationship between alength of material and an element operating thereon, the combination ofdriving meansv for said material, a position-determining device, adriving motor therefor, a generator mechanically connected to saiddriving means, connections for connecting said generator in a localcircuit with said driving motor so that the speed of said motor willvary directly with variations in the speed of said generator, a drivingmeans for said operating element, and means actuated in accordance withthe position of said element and cooperating with said positiondetermining device for controlling one of said driving means toestablish a predetermined positional relationship between said length ofmaterial and said element.

9. The method of predetermining the length of the first crop of a stripof material arranged to be driven through a rotary shear which consistsin determining the angular position of said shear with respect to theleading end of said material which will establish the desired length ofcrop, comparing the actual position of said shear therewith when saidstrip is a predetermined distance therefrom, and varying the angularposition of said shear with respect to said leading end of said stripuntil the desired angular position is obtained.

10. The method of establishing a predetermined relationship between anapparatus arranged to perform operations on a moving strip thecombination of a position-sending device driven by each of said objects,a differential position-receiving device electrically connected to saidsending devices, means for stopping one of said position-sending devicesin a predetermined angular position, and means for varying theelectrical relationship between said one sending device and saidreceiving device.

THOMAS R. RHEA. LEONID a. U'MANSKY.

